Abstract: We present measurements of two-particle correlations with neutral pion
trigger particles of transverse momenta $8 < p_{\mathrm{T}}^{\rm trig} <
16~\mathrm{GeV}/c$ and associated charged particles of $0.5 <
p_{\mathrm{T}}^{\rm assoc} < 10~\mathrm{GeV}/c$ versus the azimuthal angle
difference $\Delta\varphi$ at midrapidity in pp and central Pb-Pb collisions at
$\sqrt{s_{\mathrm{NN}}}=2.76$ TeV with ALICE. The new measurements exploit
associated charged hadrons down to $0.5~\mathrm{GeV}/c$, which significantly
extends our previous measurement that only used charged hadrons above
$3~\mathrm{GeV}/c$. After subtracting the contributions of the flow background,
$v_2$ to $v_5$, the per-trigger yields are extracted for $|\Delta\varphi|<0.7$
on the near and for $|\Delta\varphi-\pi| < 1.1$ on the away side. The ratio of
per-trigger yields in Pb--Pb to those in pp collisions, $I_{\mathrm{AA}}$, is
measured on the near and away side for the $0$--$10$\% most central Pb--Pb
collisions. On the away side, the per-trigger yields in Pb--Pb are strongly
suppressed to the level of $I_{\mathrm{AA}} \approx 0.6$ for
$p_{\mathrm{T}}^{\rm assoc} > 3~\mathrm{GeV}/c$, while with decreasing momenta
an enhancement develops reaching about $5$ at low $p_{\mathrm{T}}^{\rm assoc}$.
On the near side, an enhancement of $I_{\mathrm{AA}}$ between $1.2$ at the
highest to $1.8$ at the lowest $p_{\mathrm{T}}^{\rm assoc}$ is observed. The
data are compared to parton-energy-loss predictions of the JEWEL and AMPT event
generators, as well as to a perturbative QCD calculation with medium-modified
fragmentation functions. All calculations qualitatively describe the away-side
suppression at high $p_{\mathrm{T}}^{\rm assoc}$. Only AMPT captures the
enhancement at low $p_{\mathrm{T}}^{\rm assoc}$, both on the near and away
side. However, it also underpredicts $I_{\mathrm{AA}}$ above $5$ GeV/$c$, in
particular on the near-side.